








































































































































Class 

Book.. 


Copyright N?. 


Tiicm. 

'■ k i 

iain 


COPYRIGHT DEPOSIT. 



A 








Directions for 
Designing, Making, and 
Operating 

High-Pressure Transformers 

SECOND EDITION 



BY 


PROFESSOR 


USTIN 


Second Edition Copyright 1917 by F. E. Austin 


Copyright 1914 by F. E. Austin 


Professor and Head of the Department of Electrical Engineering 
in the Thayer School of Engineering, connected with Dartmouth 
College, Hanover, N. H. 


Author of “Preliminary Mathematics” 


“Examples in Magnetism” 
“Examples in Alternating-Currents” 
“Examples, in Battery Engineering’ 



“How to Make Low-Pressure Transformers 



1 K27 1 

Important New Books fa 



$ 1.20 


PRELIMINARY MATHEMATICS, postpaid 


This is the most instructive and valuable book ever published to 
assist Grammar and High School students, who are studying Alge¬ 
bra. It is also especially adapted for the use of those who desire to 
study mathematics without the help of a teacher, and for use in 
“Junior High School.” 

Really a complete course of instruction in the fundamentals of 
Mathematics, showing methods and practical applications. Many 
Algebra problems are all worked oat step by step. Also College en¬ 
trance exams, completely solved. 

EXAMPLES IN BATTERY ENGINEERING; postpaid $1.25 

Treats of all kinds of primary and storage cells and their applica¬ 
tions in practice. Many illustrations showing clearly how to make 
battery connections for all kinds of service; from automobiles to sub¬ 
marines. No book like it has ever been published. It is in a distinct 
class by itself. Every operator of an automobile should possess a 
copy. 

“HOW TO MAKE LOW-PRESSURE TRANSFORMERS,” 

postpaid, 40 cents 

Fifth Edition in Spanish, postpaid, 50 cents 

Tells in simple language just how to make different types of trans¬ 
formers, that can be operated from 110 and 220 volt alternating- 
current service mains. Information is given for utilizing discarded 
“tin cans” for core material in transformers. Coming generations 
will connect tin cans to electrical circuits instead of to dogs’ tails. 

READY SOON 

GENERATOR AND MOTOR EXAMPLES, postpaid, $2.00 

A scientific application of fundamental principles to engineering 
practice. Financial efficiency carefully considered. 

Remit amount with order to: 


PROF. F. E. AUSTIN, 

Box 441, Hanover, N. H. 





Designing , Making , and Operating High-Pressure Transformers 3 


TABLE OF EQUIVALENTS OF LENGTH, AREA AND VOLUME. 

1 INCH = 2.54 CENTIMETERS. 

1 centimeter = ^.54 = 0.393 inch. 

1 SQUARE INCH = 04 2 = 6.45 SQUARE CENTIMETERS. 

1 square centimeter = =0.155 square inch. 

1 CUBIC INCH = 04 3 = 16.38 CUBIC CENTIMETERS. 

1 cubic centimeter = T 8 \S¥ = 0.06105 cubic inch. 

1 MIL = txtW °f an inch. 

1 square mil = area of a square, 1 mil on a side. 

1 circular mil = area of a circle, 1 mil in diameter. 

= area of a circle of an inch in diameter. 

A square mil is greater than a circular mil, because the area of a square 
is more than the area of an inscribed circle. 

1 square inch = 1000 X 1000 = 1 , 000,000 square mils. 

4 V 1000000 

1 SQUARE INCH = - = 1,274,500 CIRCULAR MILS. 

7r 

7 r = 3.14159 = ratio of the circumference of any circle to its di¬ 
ameter. The diameter of any circle multiplied by 3.14159 = its circum¬ 
ference. 

Square root of 2 = ]/2 = 1.414. 

1 Horse-power = 33000 foot-pounds per minute = —= 550 foot¬ 
pounds per second. 

= 746 watts. 

1 Foot-pound = 1.3562 X10 7 ergs. 

Volts X Amperes = Watts. 



4 Designing, Making, and Operating High-Pressure Transformers 

DIRECTIONS FOR DESIGNING, MAKING, AND OPERATING 
A HIGH-PRESSURE TRANSFORMER. 

Introductory. 

Electric power, at a high pressure, is at present a commercial demand 
and necessity; the considerations in favor of direct-current power at high 
pressure are, with the present forms of construction, fewer than those 
favoring alternating high pressure power. The one consideration above 
all others in favor of “ alternating-current” power, is the simplicity, and 
economy with which the alternating-pressure, (constituting one factor 
of the power) may be increased or decreased in magnitude; or in common 
engineering parlance :— u stepped up” or u stepped down”, from a low to a 
high or from a high to a low value respectively. 

The device employed to accomplish the stepping up or stepping 
down process is the so-called transformer, which is a really wonderful 
piece of apparatus, when considered as an energy device. 

It should be remembered that a transformer cannot be operated 
on direct-current circuits; but only by being connected with circuits in 
which the current is continuously undergoing regular changes in value; 
that is, by alternating-currents. 

The term “ transformer” is perhaps a misnomer when used in con¬ 
nection with the now common device; since energy is not transformed 
by the device from on e form into another form; but a certain percent of 
the electrical energy supplied to the device is given out by it with simply 
a change in the magnitude of the two factors of electrical power:—pressure 
and current. The device might more aptly be called a transmuter ; from 
the Latin trans (meaning across) and mutare, (meaning to change across 
or to carry over). 

The electric power is simply carried across, through the medium 
of the so-called transformer, from one electric circuit to another. 

A transformer might then be defined as a device for the exchange of 
electric power from one alternating-current circuit to another, with a 
desired change in electric pressure. 

As will be evident later, a transformer consists essentially of two elec¬ 
tric circuits interlinked by a magnetic circuit. A chain consisting of three 
links, the middle link representing the magnetic circuit, and the two outer 
links representing the two electrical circuits; one the primary and the 
other the secondary. Since a chain is no stronger than its weakest link, so 
the commercial value of a transformer is determined by its weakest part. 

The mechanical simplicity of a transformer is remarkable; containing 
no moving parts', and although at times receiving and delivering energy 
at the rate of thousands of horse-power, it requires very little care and 
maintenance. 



There are two general types of transformers in use at present, classified 
according to their construction. One is called the “shell” type the other 
the “core” type. 

The shell type is shown at (a) figure 1, page 5, and the core type is 
shown at (b) same figure. In the shell type the iron core surrounds the 
copper circuit; while in the core type the copper circuit surrounds the iron 
core. 



Fig. 2. 


































6 Designing, Making, and Operating High-Pressure Transjormers 

The analysis of the physical phenomena involved in the operation 
of a transformer, is as complex as the device itself is simple. 

A brief explanation of the physical principles involved in the opera¬ 
tion of a transformer may be useful. 

Suppose C, in figure 2, denotes a number of thin iron plates, placed 
one above another to form a rectangular ‘‘core”. These thin plates may 
be electrically insulated from each other by insulating paint, varnish, or 
simply by a coating of iron rust that readily forms after the plates have been 
covered with moisture. 

Next suppose a number of turns of large size, cotton covered, copper 
magnet wire, denoted by P, are wound around one limb of the core, and 
a larger number of turns of smaller cotton covered copper magnet wire, 
denoted by S, are wound around the opposite limb of the core. There 
is then no electrical connection of any kind between the two coils and the 
iron core, or between the two coils themselves 

The few turns of large wire, P, may be designated as the “primary” 
while the coil consisting of many turns of small wire, denoted by S, may 
be designated as the “secondary ”. 

The primary in this case has a low resistance, while the secondary 
has a much greater resistance. 

Suppose an alternating-pressure denoted by E p is applied to the ter¬ 
minals of the primary. An “alternating-current” then exists in the primary 
which sets up an alternating magnetic flux or magnetic field in the iron 
core. This alternating magnetic flux induces a counter electromotive 
force in the primary and also induces an electromotive force in the second¬ 
ary windings. The induced electromotive force per turn of wire is practic¬ 
ally the same in both the primary and the secondary. However the 
(induced) pressure E s between the terminals of the secondary is n times 
as great as the pressure (E p ), applied to the terminals of the primary, 
if the secondary turns are n times as many as the turns on the primary. 
If E p is an alternating pressure, then E s will also be an alternating pressure. 
This does not imply that the shapes of the primary and secondary pres¬ 
sure curves are similar. Neither does it follow that the shapes of the pri¬ 
mary and secondary currents are the same. 

If now the secondary terminals are connected with a straight wire 
having considerable resistance, a current in the secondary windings will 
result, which is an alternating-current having the same frequency as the 
frequency of the applied primary pressure. The secondary current exist¬ 
ing in the secondary windings, reacts to reduce very slightly the magnetic 
flux in the core; this reduction of flux reduces the counter electromotive 
force in the primary, allowing an increase in the primary current. If 


Designing , Making , and Operating High-Pressure Transformers 7 

the resistance connected with the secondary is reduced , an increase of sec¬ 
ondary current results, with a corresponding increase of primary current. 

The operation as described, constitutes inherent regulation of sup¬ 
ply and demand, performed without the movement of a material substance 
or of mass. 

The primary acts as a “choke” coil, the value of the current in it being 
expressed by: 

-p 

I p = — p - (1.) In this equation E p denotes the applied 

1 / R 2 p+ (2xf L) 2 

primary pressure, in volts; I p the primary current, in amperes; / denotes 
the frequency, in complete cycles per second, of the applied pressure, and 
of the primary current; R P denotes the resistance of the primary winding, 
in ohms, and L denotes the so-called “coefficient of induction ,” expressed 
in “ henrys” which is the only variable in the equation. 

To show the effect the value of L has on the primary current, suppose 
the following data are given, to find I p . 

DATA. 

jr = 3.14159 

R 2 P = TOtf 

2tt/L = 377 (very nearly). 

L = 1 henry. 


E p = 110 volts 
/ = 60 cycles. 
R p = X V ohm. 


110 110 

Then I p = — : = r = .-=1 

VtU + 377 2 1/142129.01 

= 0 29 ampere. 

If to this primary winding a direct-current pressure of 110 volts should be 

applied, the resulting current would be: I p = = 1100 AMPERES, 

which would have been the same with the alternating-pressure of 110 volts, 
if the primary wire had been laid out straight with no iron near it. 

This shows the “choking” effect, on alternating-currents , of coiling a 
wire around an iron core, and the primary of a transformer is said to act 
as a “choke” coil. 

To explain somewhat differently a few of the important functional 
phenomena occurring during the operation of a transformer, a brief outline 








8 Designing, Making, and Operating High-Pressure Transformers 


treating of a particular case in designing, is included in the following dis¬ 
cussion applying to transformers. 

While it is possible the mathematical discussion may not be com¬ 
pletely comprehended by one who has had only a limited training in 
“mathematics”, it is hoped that everyone may obtain valuable informa¬ 
tion regarding the general principles of transformer operation by carefully 
studying this portion of the text. 

For the benefit of those desiring to build a high pressure transformer 
for experimental use, such as for wireless telegraphy, for the production 
of “ozone” or for vacuum tube lighting, data applying to specific cases 
are given. 

If however, one studies carefully the general principles, many varia¬ 
tions from the given conditions may be readily effected, to meet a large 
range of requirements. 

The matter headed “CAUTION” and “PRECAUTION” should 
be very carefully read by everyone who builds or who operates a high- 
pressure transformer. 


SYMBOLS AND NOTATION. 


Since electric power is often expressed in terms of the two factors, 
pressure and current, denoted by E X I, (meaning the product of a pres¬ 
sure, in volts, by a current, in amperes) if that portion (or link) of the trans¬ 
former to which the electric energy is supplied is designated as the “pri¬ 
mary”, while that portion (or link) from which electric energy is delivered 
is called the “secondary”, the following symbols and notation will be adopt¬ 
ed. 

E p denotes the pressure, in volts, applied to the primary circuit. 

E s denotes the pressure, in volts, available from the secondary circuit. 

I p denotes the current, in amperes, in the primary circuit. 

I s denotes the current, in amperes, in the secondary circuit. 

R p denotes the resistance, in ohms, of the primary circuit. 

R s denotes the resistance, in ohms, of the secondary circuit. 

W p denotes the power input, in watts, to primary circuit. 

W u denotes the useful power output, in watts, from secondary. 

-q (Greek letter eta) denotes the so-called commercial efficiency of a 
transformer. 


Then: rj 


W„ 

Wp 


; (2): being a symbolic expression for the commercial 


power efficiency of any transformer. 

The commercial power efficiency of a transformer is the ratio of 
the useful power output to the total power input. 



Designing , Making , and Operating High-Pressure Transformers 9 


If a transformer is operating a load consisting of incandescent lamps, 
as is common practice, then the commercial efficiency of the transformer 
might be expressed by: 


v 


Esls 

w7 


; (3). 


If the output from a transformer is increased, the input must also be 
increased. The input has always to supply the output plus all the losses. 


LOSSES IN A TRANSFORMER. 


The losses in a transformer may be divided into the “ copper losses” 
and the “ core losses”. The copper losses may be still further divided into 
the loss in the primary windings and the loss in the secondary windings. 
These are the so-called RI 2 losses, in watts. The primary loss would be 
expressed by R P I P 2 and the secondary loss by R S I S 2 . The resistances R p 
and R s of the primary and secondary coils respectively, are constants *; 
while the currents denoted by I p and I s are variables. The copper losses 
are therefore variables, depending upon the load output. If there is no 
load output, then I s is zero and R s I a 2 is also zero. If the transformer has 
its primary connected with service mains, even with no load output, there 
will be some R P I P 2 loss in the primary. However under this condition, 
the primary current I p is very small; less than unity, so that the square of 
the current will be still less,f numerically, and R p being not much greater 
than unity, (usually less than unity) the R P I P 2 loss for small transformers, 
is usually less than one watt at no load secondary. When however a load 
is applied to the secondary, then the R S I S 2 loss in the secondary becomes 
appreciable, the R P I P 2 loss in the primary increases, and the total copper 
loss becomes large enough to be a considerable proportion of the total 
power input. It is evident then as the load output increases, the primary 
and secondary currents increase, causing the total copper loss, expressed 
by R P I P 2 + R s Is 2 to increase. 

CORE LOSSES IN A TRANSFORMER. 

The so-called “core loss” in a transformer may be divided into the 
“eddy current” loss and the “hysteresis” loss. The eddy current loss is an 
R I 2 loss, produced by currents induced in the iron core by the primary 
input.* To reduce the eddy currents, and the eddy current loss, the core is 

*So long as the temperature of the coils remains constant. 

fFor example, \ is less than unity, and the square of 2 is I; less than J. Likewise the 
square of j is & •, which is less than f. 




10 Designing , Making, and Operating High-Pressure Transjormers 


made u laminated”, built up of thin plates of iron, insulated from each other; 
usually by varnish. 

The hysteresis loss is a heat loss produced by the reversals of the 
molecules of the iron in the core when the magnetism of the core is reversed; 
which happens every time the current in the primary is reversed; for a 60 
cycle circuit, this happens 120 times every second. That is, the molecules 
are turned end for end 120 times every second. Such rapid movement of 
molecules produces heat, as though the iron were hammered rapidly with a 
hammer; as may be done by placing an iron nail on a rock or on an anvil 
and hammering it rapidly. The only method adopted to reduce the hy¬ 
steresis loss, is to use a “soft” iron, or one having a small hysteretic coeffi¬ 
cient. 


LOSS DUE TO HYSTERESIS. 


The numerical values of hysteretic loss, per cubic inch of iron in the 
core, as well as for any frequency/, or flux density 33, may be calculated 
from the equation: 

— 16.38 . ~ . — 

Wh = —7 K,+33 ; (4) in which Wh denotes the loss in watts; / the 

frequency of the supply pressure, in cycles per second; 33 the flux density in 
gausses, or maxwells per square centimeter, and K denotes what is called 
a hysteretic coefficient, which varies for different kinds or qualities of iron. 
For ordinary transformer steel, K = . 0021. 


Maximum In¬ 
duction per 
Square Inch 

Maximum 
Induction 
per Square 
Centime¬ 
ter 

in Gausses 

Loss in 
Ergs per 
Cycle per 
Cubic 
Inch of 
Iron 

Loss in 
Watts, at 
/= 15 Cycles 
per Second, 
per Cubic 
Inch of Iron 

Loss in 
Watts, at 
/= 25 Cycles 
per Second, 
per Cubic 
Inch of 
Iron 

Loss in 
Watts, at 
/=60 Cycles 
per Second, 
per Cubic 
Inch of 
Iron 

Loss in 
Watts, at 
/=100 
Cycles 
per 

Second, 
per Cubic 
Inch of 
Iron 

6451.6 

1000 

2170. 

.003255 

.00542 

.01402 

.0217 

12903.2 

2000 

6879. 

.01031 

.01719 

.04127 

.0688 

19354.8 

3000 

13104. 

.01965 

.03276 

.07862 

.1310 

25806.4 

4000 

20147. 

.03022 

.05038 

.1208 

.2015 

32258.0 

5000 

27846. 

.04176 

.06961 

.1670 

.2784 

38709.6 

6000 

36036. 

.05716 

.09528 

.2286 

• 3811 

45161.2 

7000 

45208. 

.07311 

.1218 

.2924 

.4864 

51612.8 

8000 

56511. 

.09070 

.1511 

.3628 

.6047 

58064.4 

9000 

68796. 

.1094 

.1724 

.4379 

.6899 

64516 

10000 

81900 

.1296 

.2160 

.5184 

.864 















Designing, Making, and Operating High-Pressure Transformers 11 


From inspection of the equation and the values in the table it may be 
seen that the loss due to hysteresis increases in proportion to the increase 
in frequency, but not in proportion to the increase in flux density. 93 is 
raised to the 1.6 power, which may be done by the use of logarithms, as 
shown on page 25. 

All of the losses in a transformer are in reality heat losses; a certain 
portion of the energy supplied to the transformer in the form of electrical 
energy, is effective in doing useful or desired work, while a certain portion 
is unavoidably changed into non-useful heat. 

In designing transformers, the aim is to keep the losses as small as 
possible consistent with the cost of construction. 

The efficiency 77 does not vary in direct proportion with the output, 
since the copper losses in a transformer are not constant for all loads. 

If the input and the output of any given transformer be measured 
simultaneously by the proper instruments, connected as indicated in figure 
3, page 12, and the output, in watts, be plotted horizontally, while the corres¬ 
ponding values of the commercial efficiency, calculated from equation (3), 
page 9, are plotted vertically as indicated in figure 4,page 13; the result, 
shows the variation in the efficiency for different outputs. The curve in 
figure 4 shows the result of a test of a T V kilowatt (about \ horse-power) 
transformer designed to transform from 110 volts, 60 cycles, to about 60 
volts, 60 cycles. This transformer is shown at d and at e in figure 5. 



Fig. 5. 

The condition expressed by: W u = E S I S , exists only for a nonin- 
ductive load, such as lamps or a liquid resistance, or any wire resistance not 
wound in the form of coils. 

The condition is changed if the load consists of motors, these being 
highly inductive. 





12 Designing , Making, and Operating High-Pressure Transformers 










































Designing, Making, and Operating High-Pressure Transformers 13 


Output in Per Gent, and Pressure in Volts. 



Output in Watts. 































































































































14 Designing, Making, and Operating High-Pressure Transformers 


When there is no useful output from a transformer, there may be some 
input, to supply the core losses, which are however not large, and moreover 
are to be considered constant irrespective of loads. That is, the power loss 
due to the core, is the same at no useful load output as at full-load or at any 
over-load output. 

This core-loss means a constant source of expense, if a transformer is 
kept connected to service mains when not supplying power output. While 
the core-loss, expressed in watts, may not be large, the watt-hour expense 
may be considerable if the transformer is connected with the service mains 
during a long time. The expense incurred in using electrical power de¬ 
pends upon two conditions, the RATE at which electricity is used, and the 
interval of time during which it is used. 

To illustrate this feature, suppose the core-loss of a transformer is 
found by measurement to be 65 watts. If the transformer is connected 
with the service mains for 10 hours while furnishing no useful output, the 
total energy used will be 65 X 10 = 650 watt hours, which at a price of 
15 cents per KILOWATT HOUR (per 1000 watt-hours) will cost X 

15 = 9f cents. If the transformer is connected all day, (24 hours) the 

65 X 24 

cost of the core-loss will be- X 15 = 23.4 cents. 

1000 

This is an important consideration for the experimenter who uses 
transformers, when the energy he uses is registered by meter, and shows 
the value of a switch, to throw the primary out of circuit except when act¬ 
ually needed to produce a useful output. 

In almost all experimental work with high pressure (step-up) trans¬ 
formers, it will be advisable to connect a double-pole “knife” switch with 
the primary, so that when this switch is opened, the useful load is dis¬ 
connected without danger of shocks to the operator and at the same time 
the no-load core-loss is eliminated. 

POWER FACTOR. 

Consulting figure 3, page 2, again, to note the arrangement of the 
voltmeter, the ammeter, and the wattmeter in the primary circuit, a few 
words explaining the meaning of “power factor” may not be amiss. 

If the primary pressure, E p , applied to the primary coils of a transform¬ 
er were a direct-pressure (direct-current pressure) the product of the volt¬ 
meter indication and the ammeter indication would be the same as the 
indication of the wattmeter; if all the instruments gave correct indications. 
The current in the primary coils would then be expressed by: 



Designing , Making , and Operating High-Pressure Transformers 15 


Ep 

= according to Ohm’s law, and the indication of the wattmeter 

XVp 

by: W p = Eplp. The direct-current in the primary coil would however 
have no effect on the secondary coil. 

When however the pressure applied to the primary is an alternating- 
pressure, the indication* of the wattmeter is no longer the same as the 
product of the voltmeter and ammeter indications, but is found to be less. 

In such a case the true input in watts is indicated by the wattmeter, 
and the relation would be expressed by: 

W p = Eplp X power factor; or as is sometimes expressed: W p = 
Eplp X P. F. (5) (P. F. stands for power factor). From either of 
these expressions is obtained: 


W 

Power Factor = — f-. ( 6 ) Since the product E P I P is usually 

Eplp 

greater than Wp, the power factor is usually less than unity. Theproduct 
Eplp can never be greater than W p , and the power factor can never be 
greater than unity. 

The power factor may vary as the load varies. 

Returning to the consideration of efficiency as expressed by equation 


(2) page 9, this may be expressed by: rj = 


Eglg 


Eplp X P. F. 


;(7). 


Now suppose that the secondary pressure is exactly equal to the primary 

Is 


pressure, then the efficiency may be expressed by rj = 


I D X P.F. 


5 (7a). 


It is a well known and commonly accepted fact that the EFFI¬ 
CIENCY of any electrical device IS ALWAYS LESS THAN UNITY; 
that is the per cent efficiency is always less than 100 %. 

Since the P. F. is never greater than unity and since 17 must always be 
less than unity it is evident from the last equation that in a transformer, 
when the primary and secondary pressures are equal, the secondary cur¬ 
rent will always be less than the primary current. 

Furthermore it may be noted that although the primary pressure and 
secondary pressure bear a certain definite relation to one another the same 


♦When dealing with instrument indications as in this discussion the indications must 
be noted simultaneously; all taken at the same instant. 





10 Designing, Making, and Operating High-Pressure Transfor 

proportionate relation cannot exist between the secondary an rimary 
currents, even if the power factor is unity. 

If the efficiency is high; nearly unity or nearly 100%, tl propor¬ 
tionality of currents and pressures is more nearly the same. r many 
practical considerations the proportionality is assumed to be le same. 
This will be made clearer by consideration of the following: 

RATIO OF TRANSFORMATION: The so-called rati 
formation has reference to the ratio of the secondary to the pri y pres¬ 
sure. The primary is that portion of a transformer to which t rimary 
pressure is applied, and the secondary is that portion of the t dormer 
producing the secondary pressure. It should be noted that tl rimary 
pressure may he greater (as in a step-down transformer) than theecondary 
pressure. The best definition of the primary of a transforn is, that 
portion of a transformer receiving energy ; this having no referen o pres¬ 
sures. 

In any case the ratio of transformation may be expressed 

RATIO OF TRANSFORMATION = 

SECONDARY PRESSURE, IN VOLTS E s 

PRIMARY PRESSURE, IN VOLTS E p 

As an example, suppose it is desired to find the ratio of tran- mation 
of a transformer, if the applied primary pressure is 2200 voi and the 
secondary pressure is 110 volts. 

RATIO OF TRANSFORMATION = = or the 

transformation is a 20 to 1 (step-down) transformation. 

Again, suppose the primary pressure is 110 volts and thsecondary 
pressure is 20,000 volts, then the RATIO OF TRANSFORM 1'ION = 
= = 181.81; or the transformation is an 11 to WO trans¬ 

formation. 

When the ratio of transformation is greater than unity he trans¬ 
former is called a “step-up” transformer ; when less than unity.: is called 
a “step-down” transformer. 

If there were no losses in a transformer, then the currents i the pri¬ 
mary and secondary coils would be in exact inverse ratio to ea t other as 
compared with their corresponding primary and secondar m'essures. 
But as indicated by equations (7) and (7a), page 15, such exrb relation 
cannot exist. 

Let it be supposed that E 8 = n times E p , then equation , page 15 
may be written: 



Designing, Making, and Operating High-Pressure Transformers 17 


Efficiency, 77 


(nEp) I 8 

Epl p X P.F- 


(9); (E s = nE p .) 



y X P. F. 
n 


or I s 


-%XP. F. (10). 

n 


That is, when the secondary pressure is n times the primary pressure, 
the secondary current is not exactty (p) one nth. of the primary current; 
since 77 X P. F. is always less than unity. 

For ordinary purposes, however, the proportional relations; if E s = 
nEp then I s = (p)I p ; may be used without great error. It should be 
remembered however that if E s is exactly n times E p , I s is always slightly 
more than p of I p , in actual practice. 

It is evident at this point in the discussion, just why the transformer 
is so valuable as an intermediate device in the process of power transmis¬ 
sion. By stepping the pressure up, the current may be stepped down, so 
that for transmitting a given power, much less line copper is necessary, 
when the power is delivered at a high pressure, (small current) than when 
the same power is delivered at a low pressure. With the smaller current 
the RI 2 line loss is greatly reduced. Interest on investment of copper is 
rendered much less by using the transformer. 


DESIGNING A 20,000 VOLT TRANSFORMER. 

In designing a transformer as in designing many electripal devices, 
different requirements as to the operative conditions will necessitate dif¬ 
ferent methods in designing. 

A brief outline applying to the design of a transformer will be pre¬ 
sented herewith that may serve as a guide ^n varying the manufacture of 
the transformer, for which working directions are given, beginning on 
page 26. The method here adopted is not a rigorous mathematical treat¬ 
ment, but* one designed to emphasize practical applications. As a matter 
of fact designs are usually figured out on the assumption that the alter¬ 
nating-pressures and currents are sine-waves, while they are seldom such 
shapes in practice. Deviation from a sine-wave form affects the whole 
matter of transformer design and operation. The considerations in this 
book will be on the assumption of sine-wave forms. 

The following outline will apply to a 1 K. W. or 1000 watt output, 
11 step-up” transformer, transforming 110 volts, at 60 cycles, to 20,000 volts, 
necessarily at the same frequency. 

The ratio of transformation is = 181.8. See page 16. 




18 Designing , Making , and Operating High-Pressure Transformers 


The primary current will be assumed as 10 amperes, and the second¬ 
ary current as . 05 ampere. 

The core losses and the full-load copper losses in the transformer will 
be assumed to be equal to a total of 75 watts, and the copper losses to be 
equal to 50 watts. This means that the efficiency of the transformer is 
to be 93%. The output being 1000 watts and the input being = 
1075.1 watts. The core losses will evidently be 25 watts total. The core 
losses consist of the so-called eddy-current loss and the hysteresis loss; 
while the copper losses are the RI 2 losses in both the primary and the 
secondary coils. 

The resistances of the primary and secondary may be readily cal¬ 
culated, for any assumed current, if the loss in the primary and in the 
secondary coils is given. 

The primary loss in watts is denoted by R P I P 2 . 

The secondary loss in watts is denoted by R s I a 2 . 

Under the given conditions R P I P 2 + R S T S 2 = 50 watts. 


RESISTANCE OF PRIMARY WINDINGS. 


Although the sum of the primary and the secondary losses is to be 50 
watts, the two losses are not necessarily equal to each other. It will be 
advisable to allow a less loss for the primary than for the secondary. 

For the case under consideration the loss for the primary will be as¬ 
sumed as 20 watts; while that for the secondary will be assumed as 30 
watts. 

Since the loss in the primary windings is to be 20 watts, then: 

20 

R P I P 2 = 20, and R p = = T 2 ^ = 0.2 ohm, the required re- 

10 2 

sistance of the primary windings. 

NUMBER OF TURNS IN THE PRIMARY WINDINGS. 


At this point it will be necessary to present what is called the funda¬ 
mental equation of the transformer. Expressed in symbols this is: 


Ep 


A c Np x 2 tt/93 

1/2 10 * 


(11) in which E p denotes the alternating- 


pressure, expressed in volts, applied to the primary; A c denotes the area, 
expressed in square centimeters, of the cross section of the iron core; N p 
denotes the number of turns in the primary windings; / denotes the fre¬ 
quency, in cycles per second, of the applied pressure, and S3 denotes the 
number of magnetic lines of force set up in the core per square centimeter 
of cross section of the iron core. 



Designing , Making , and Operating High-Pressure Transformers 19 


So far as the assumptions already made are concerned, there are three 
unknovms in this equation; A c , N p , and 58. E p = 110 volts, / = 60, 
and 2 tt = 2 X 3.1416. 

If values are assumed for A c and 58 the equation may be solved for the 
value of N p ; the number of turns of wire in the primary windings. 

It is not advisable to allow the value of 58 to exceed 5000 gausses 
(magnetic lines per square centimeter) in transformer operation. 

It is plain that the greater the value assumed for 58, the less number of 
turns will be required, and the less iron required for the core. 

Let 58. = 3000 and A c = 44.4 centimeters. Then: 

10 8 X E p 11,000,000,000 _ 

P ~~ 1/2tt/58A c = 1.414 X 3.1416 X 60 X 3000 X 44.4 

= 300 TURNS. 

DATA. 

To 8 = 100,000,000. 

E p = 110 volts. 

, / = 60 cycles per second. 

1/2 = 1.414; 1/2t r = 4.44; ]/2t rf = 266.53. 

LENGTH OF THE PRIMARY WINDINGS. 

If the cross section of the iron core is to be 44.4 square centimeters 
it will be = 6.89 square inches. 

If the core is to be square in cross section, the length of one side must 
be J/6.89 = 2.6 inches. The distance around the core will be 4 X 2.6 
= 10.4 inches. 

The length of a mean turn of the primary must be more than this, say 
11 inches. If there are 300 turns in the primary windings the total length 
will be 300 X 11 = 3300 inches or- 3 -f§ iL = 275 feet. 

SIZE OF THE PRIMARY WIRE. 

If the resistance of the primary is to be T 2 ^ ohm, (page 18) and its 
length 275 feet, the resistance per foot must be = 0.000727 ohm. 

Consulting the table on page 21 column headed I, the nearest size 
of Brown & Sharp gauge wire is found to be a No. 9 wire. 

WEIGHT OF THE PRIMARY WINDINGS. 

Since No. 9 B.& S. gauge double cotton covered round copper wire 
weighs 0.0404 pound per foot in length, the weight of the complete primary 
winding will be 0.0404 X 275 = 11.1 pounds. 




20 Designing, Making, and Operating High-Pressure Transformers 


DATA APPLYING TO THE SECONDARY. 

NUMBER OF TURNS IN SECONDARY WINDINGS. 

The ratio of transformation being 181.8 and the number of primary 
turns being 300, the minimum number of turns required for the secondary 
would be 181.8 X 300; but if the ratio of currents is assumed inversely 
as the pressure ratios, then there must be more than the proportionate 

181 8 X 300 

ratio of turns. At least —— : - = 58645 TURNS. 58650 MAY 

.93 

BE ALLOWED. 

RESISTANCE OF SECONDARY WINDINGS. 

Since the loss in the secondary has been assumed at 30 watts, then the 
resistance, in ohms, of the complete secondary windings will be: 

R s = — 7 = ^ = 12,000 ohms. 

.05 2 .0025 

LENGTH OF THE SECONDARY WINDINGS. 

The current density assumed for the secondary wire being 1032 am¬ 
peres per square inch, which has been found to be a safe value, from the 
relation, 

7 ^ = 1032, the area of the secondary wire will be A s = tt/WV or 
As 

.00004845 square inch. 

The area of this wire, in circular mils, will be, .00004845 X 1,274,500 
= 61.7 CIRCULAR MILS. (See page 3.) 

The nearest B. & S. gauge wire is a No. 32, (see table page 21, column 
D.) which will be used. 

If No. 32 B. & S. gauge is used and the total resistance of the secondary 
is to be 12000 ohms, the possible number of feet will be: 

1 f§xt = 74165 FEET. (From column I page 21, No. 32 wire has 
a resistance of . 1618 ohm per foot.) 

WEIGHT OF SECONDARY WINDINGS. 

Consulting table on page 21, column headed G, the weight of double 
cotton covered, 32 B. & S. is seen to be .222 pound per 1000 feet. The 
total weight required in the present case is .222 X 74.16 = 16£ 
POUNDS. 




Those desiring to design transformers for outputs different from those given in this book, will find the data, applying 
to the more common sizes of round Double Cotton Covered (D. C. C.) copper magnet wire, of considerable help to them. 


Designing , Making, and Operating High-Pressure Transformers 2 


*“5 

Ohms per Foot 

at 122 degrees 

F. 

.0004406 

.0007007 

.0008835 

.001114 

.001771 

.002817 

.004964 

.007122 

.01132 

.01801 

.02863 

.04552 

.07239 

.1151 

.1830 

.2910 

.4627 

.7357 

1.296 

- 

Ohms per Foot 

at 68 degrees 

F. 

.0003944 

.0006271 

.0007908 

.0009972 

; .001586 

.002521 

.004009 

.006374 

.01014 

.01612 

.02563 

.04075 

.06479 

, .1030 

.1618 

.2605 

.4142 

.6585 

1.047 

M 

Feet per Pound 
of D. C. C. 
Wire 

© l> 1-1 <N 1C 

(Na^HQNMINOCOCi^OHOOfflNON 

1—ii—INC01<MNO)ONMHOHOONCOHM 

1-1 1 -t CO ^ H N to N CC O M 

H H IN M U5 N H 

O 

Weight per 
1000 feet of 

D. C. C. Wire 

(MtONINOOHCDOO 

0)«5INMO(N(NCO(N^OCO^ 

i-HTtHT^CirHt^®>0<NOCOOOlOCO<Ni-Hi-H©0 

O O O H o (N N lO'CO (N H 

00 1C rf M N H 


Diameter of 
D. C. C. Wire 
over all in in. 

WHOlOOCiCCHOOH 

OlMiOMlNiOOOH^O^HOHDiOCCiHH 

^^-i^^hqoooooooooooooo 

W 

Area in 
Square 

Inches 

.020612 

.012969 

.010279 

.0081553 

.0051276 

.0032271 

.0020268 

.0012756 

.00080425 

.00050273 

.00031731 

.00019856 

.00012469 

.000078540 

.000049639 

.000031173 

.000019635 

.000012316 

.0000077437 

Q 

Area in 
Circular 

Mils 

26,244 
16,512 
13,087 
10,384 
6,528 
4,106 
2,583 
1,624 
1,022 
642.4 
404.0 
254.1 
# 159.8 
' 100.5 
63.2 
39.69 
25.00 
15.72 
9.88 

O 

Diameter 

in 

Mils 

O0 <N CO *0 Tf rtlCOtO CD ^ 

i0^®00O00C0OC0H03CDO05MO0)H 

NOO^hO^OOhiOOiONONCOiOCOM 

COINHOOOCOO^CONNHHH 

« 

Diameter of 

Bare Wire 
in Inches 

O0 <N CD IQ O ^ ^ CO 1C CD 

OiO^OlOOOCOC005WH05CDOOlCOOO)H 
o5a0''tf’—lO'^OOi-iiDOiDCNOt^COiOC'OC'O 
® N H O OO CO- tO^POCNCNi—ii-Hi— IOQQO© 
^y^^OOOOOOOOOOOOOOO 


No. 

B.&S. 

Ga’ge 

COOOOO(N^CDOOO(N'^COOOOiMt)<CDOO© 

^^"HHHHHDINOiCiDlCOCOCOCOCO^ 


























22 Designing, Making, and Operating High-Pressure Transjormers 

DESIGNING THE IRON CIRCUIT. 

The iron circuit of a modern transformer consists of thin plates of soft 
steel, sometimes called “transformer steel”, laid one upon another to form 
an iron core of the desired thickness; denoted by C in figure 2, page 5 and 
figure 17, page 37. The plates are usually coated all over with some kind 
of insulating varnish, to insulate each plate from the ones next to it; thus 
reducing the loss due to so-called “eddy-currents”; (also called “foucault 
currents”). 

While joints are undesirable, so far as losses in the iron magnetic 
circuit are concerned, it is very difficult to construct a high-pressure trans¬ 
former without joints, and a magnetic circuit without joints increases the 
first cost of material, because of the waste material in stamping the plates, 
and increases the cost of labor in assembling. 

The softer the iron or steel that is used for the core, the less the loss 
due to “hysteresis”. Ordinary iron plates may have their magnetic 
qualities improved by “annealing”; heating them to a red heat and allow¬ 
ing them to cool very slowly while protected from the air by being covered 
with ashes. Hysteresis loss being due to the reversal of the molecules of 
the iron when the current in the primary coils is reversed, if the frequency 
of the primary current is increased, the molecules of iron have their position 
reversed more times each second, and the more rapid motion of the mole¬ 
cules has the effect of increasing the heating of the iron core; as more rapid 
hammering would have. The higher the frequency the greater the “hy¬ 
steric” loss. 

The heating of the core means the appropriation of a portion of the 
energy input to the transformer that is therefore not available for useful 
output, and which should be kept down to as small an amount as possible. 





















Designing , Making , and Operating High-Pressure Transformers 23 

NUMBER OF IRON PLATES FOR GORE. 

If the core is built up of plates 2\ inches wide; one set being 12^ inches 
long and the other set 1\ inches long as indicated in figure 6, the plates 
being tMit of an inch (15 mils) thick, it would require about 168 sheets 
placed together flatwise to build up to a thickness of 2\ inches. With a 
width of 2\ inches the thickness should be slightly over 2\ inches (2£ 
inches) to make the cross section of the core 6.89 square inches as stated 
on page 19. 

As will be shown later, on page 25, this cross section is slightly less 
than is necessary to give the volume of iron for continuous operation at 
full-load under the assumed conditions. 

There will be needed, 2 X 183 = 376 sheets Y2\" by 2\" by 15 
mils thick, and the same number of sheets 7\" by 2\" by 15 mils thick, 
to build up the core. If thicker material is employed a less number of 
sheets will be needed. Also the sheets might be wider as shown in figure 7, 
page 22. 


WEIGHT OF THE IRON CORE. 

The total volume of the iron core as given above will be 2\ x 2f x 40 = 
275 cubic inches. The mean length of the magnetic circuit is 40 inches. 
If the iron weighs 0.27 pound per cubic inch, the weight of the core is 275 
X 0.27 = 74 pounds. 


DESIGNING THE IRON CIRCUIT. 

CORE LOSSES. 

A consideration of the core losses from the application of the results 
of experimental practice will be in order. 

The total volume, in cubic inches, of the iron constituting the core of a 
transformer is found by multiplying the mean length, in inches, of the 
magnetic circuit, by its cross sectional area, in square inches. The volume 
of the core will be expressed by: 

V = A c l (cubic inches). V denoting volume in cubic inches; A c 
area of cross section of iron core in square inches, and l the mean length of 
the magnetic circuit, in inches. The mean length of the magnetic circuit 
shown at C figure 7, page 22 is 46 inches. This shows holes punched in the 
core sheets to allow bolts to be passed through, to bolt the sheets firmly 
together. 


24 Designing, Making, and Operating High-Pressure Transformers 


The eddy-current loss per CUBIC INCH of core, when made of thin 
plates, as found by careful experimentation, may be expressed by: 

C2 S2 m2 

We = 16.38 — # , 6 - (12) 

in which equation, W e denotes watts, b denotes the thickness of the iron 
plates, IN MILS; that is in thousandths of an inch; / denotes the fre¬ 
quency of the primary current, and necessarily of the magnetic flux in the 
iron core; 58 denotes the flux density, in gausses; that is in maxwells per 
SQUARE CENTIMETER. The flux density per square inch in the pre¬ 
sent case is 3000 X 6.45* = 19350 maxwells. Substituting the proper 
numerical values in the above equation gives: 

= 225 X 3600 X 9,000,000 

e “ ' 10 , 000 , 000 , 000 , 000,000 

1.638 X 2.25 X 3.6 X 9 119.4 

10,000 “ 10,000 

= .01194 WATT. 


DATA. 

b = TTJiFtf inch. 

= 15 mils. 

b 2 = 225. 

/ = 60. 

f = 3600. 

58 = 3000 GAUSSES. 

5B 2 = 9,000,000. 

It may be noted that 10 raised to the 16th. power, is expressed by 
writing 1 with sixteen ciphers after it. Multiplying 10 by itself 16 times 
will prove the result. 

The loss per cubic inch expressed in watts, due to hysteresis, may be 
expressed by: 

16.38K/58 1 - 6 . 

Wh = --; in which equation/and 58 have the same mean¬ 

ing as previously; (see equation ( 11 ) page 18.) while K denotes a so-called 
hysteretic constant; equal to about 0.0021 for ordinary thin transformer- 
steel sheets. 

*6.45 square centimeters equal one square inch. (See page 3.) 






Designing , Making , and Operating High-Pressure Transformers 25 


Substituting the proper numerical values gives: 

_ 16.38 X 0021 X 60 X 3000 16 
h ~~ 10 , 000,000 
= 1.638 x .0021 x 6 X 3.65 = .07533 WATT. 


DATA. 

K = .0021. 

f = 60. 

_© = 3000. 

log 93 1 - 6 = 1.6 X log 3000. 
log 3000 = 3.477121 
1.6 


20862726 

3477121 


Therefore log $ 8 1,6 
and 3000 16 


5.5633936 

365000. 


The total CORE LOSS IN WATTS PER CUBIC INCH is therefore: 

W e + W h = 0.01194 + 0.07533 = .08721 watt. 

If the assumed core loss is to be 25 watts the necessary volume of iron 
will be: = 286 CUBIC INCHES. 

This is the minimum allowable volume for continuous operation at 
the assumed core loss. 

It may be noted that the length of the core must be proper to accom¬ 
modate the requisite number of turns of wire, both primary and secondary, 
as well as the necessary amount of insulating material, separating the 
primary from the secondary, and separating the sections or so-called 
“pies” of the secondary winding. 

The so-called “core type” of transformer is always adopted for high- 
pressure work; see b, figure 1, page 5. 

To obtain an idea of the necessary space required for the windings of 
the transformer being designed, again consulting the table on page 21 , 
the diameter of No. 9 covered wire, (column F) being .125 inch, and there 
being 300 turns, the cross sectional area required by the primary windings 
is 0.125 X 0.125 X 300 = 4.68 square inches. 

For the secondary the required area is 0.0169 X 0.0169 X 58650 = 
16f square inches. 

A total of about 21 £ square inches is required for both windings. If 
the primary is wound in two layers, and one section for each limb of the 







26 Designing , Making , and Operating High-Pressure Transformers 

core, the necessary length of core to accommodate one section of two layers 
will be X 0.125 = 9.4 inches. The distance may be made 10 
inches as indicated in figure 6, page 22. 

Allowing 50% of area for cross-section of insulation, the area included 
by the core will need to be about 42 square inches. If the opening through 
the core, is 10 inches in one direction, the other dimension of the opening 
(or the width) will need to be 4.2 inches. This should be taken as 5 
inches, when building the core; see figure 6, page 22. 

DIRECTIONS AND DATA FOR CONSTRUCTING A 3 KILOWATT, 
20,000 VOLT TRANSFORMER. 

The following directions and data will enable anyone to construct a 
transformer for use on a 60 cycle alternating-current circuit, that will give 
an output of about 3 kilowatts continuously without overheating, or a 50% 
greater output for short intervals, with a pressure of 110 volts applied to 
its primary, while delivering the output at about 20,000 volts. 

IRON CORE. 

196 strips of soft iron (so-called Russia iron that stove pipe is made of 
will serve well; or so-called “transformer steel” may be used) 9? inches 
long by 2\ inches wide, and 196 strips of the same material 15| inches long 
by inches wide; all 4V of an inch thick. 

The data applying to the iron core is here given differently than that 
given under the “Design of a 20,000 Volt Transformer” for the reason that 
many who desire to construct a transformer cannot readily obtain the thin 
“transformer steel”, but are able to obtain the “Russia” iron from local 
hardware dealers. This iron comes usually about 43- of an inch thick in 
large sheets, from which, strips of the desired size may be cut. The strip 
should be kept as flat as possible. 

1. Carefully remove all burrs and sharp edges from the iron strips 
by means of sand paper (No. 0), or by means of a fine file. 

2. Coat both sides and edges of each strip with shellac varnish. 

3. Stand strips on end as soon as varnished and allow the varnish 
to dry for several hours. One side of each strip may be varnished and 
allowed to dry thoroughly, and then the other side may be treated likewise. 
The drying process should take place in a warm dry room. 

4. Do not allow one freshly varnished strip to come into contact 
with another strip while drying. 

5. While the strips are drying, prepare the wooden supporting 
structure according to the following: 


Designing , Making , and Operating High-Pressure Transformers 27 


A base consisting of soft pine, made of planks 22 inches long, 2 inches 
thick and of sufficient number (depending upon their width) to form a base 
22 inches X 22 inches. These planks to be cleated together by screwing 
to their under sides two cleats of the same material, 2 inches thick, 22 inches 
long and 4 inches wide. See figure 8. 




Fig. 9. 


Fig. 10. 








28 Designing , Making , and Operating High-Pressure Transformers 



The lumber used should be planed on both sides and edges. 

If the completed transformer is to be moved about, from one place 1 
another, very frequently, the base should be provided with heavy caster 
which may be secured to the under surface of the cleats. “ Feltoid 
casters, made by the Burns and Bassick Co., Bridgeport, Conn., have bee 
found to give the best satisfaction. Four of these are sufficient: one fc 
each corner of the base. As the completed transformer weighs about 14 
pounds it will be well to “block up” the base to relieve the casters of th 
weight, when not being transported. 

6 . Provide two soft pine pieces, each 19 inches long, 2\ inches wide, 
and 3 inches high as indicated at M and M', figure 8, which when properly 
located on the top of the plank base, serve to provide a bearing surface for 
the iron core of the transformer. The proper position for the bearing 
pieces may be seen by consulting figure 8, page 27. 

7. Bore four holes,* two of which are indicated by h', and h", T 9 ^ 
inch in diameter, completely through the supporting blocks, M, M', the 
board base and the cleats. The distances between the supporting pieces 
and between the centers of the holes are given in figure 8. 

8 . Two strips of hard wood, (oak or maple) each 16 inches long, 2\ 
inches wide and 1 inch thick, as indicated by S, and S', figure 9, should be 
provided with holes to coincide with those in the supporting blocks. 

*Care should be taken not to put screws in the cleats and base where it is necessary to 
bore the holes. 






Designing, Making, and Operating High-Pressure Transformers 29 

These strips serve to bind the iron strips firmly together by means of 
four bolts, 12 inches long and § inch in diameter, which pass down on either 
side of the iron core, through the supporting pieces, and the base, two of 
v jch are shown in figure 9, at b and b'. 

J 9. If desired, sand paper the surfaces of the wooden structure, and 
,in with cherry or oak stain as preferred. Apply with a brush a “filler” 
sisting of \ pint of linseed oil, \ pint turpentine and about two table- 
tonfuls of corn starch thoroughly mixed together. After the two appli- 
ions have dried for 24 hours, rub the surface with a handful of excelsior, 
remove lumps and excess of corn starch, and apply a coat of shellac 
rnish. After this has dried for 10 hours, sand paper the surface with 
>. 00 sand paper, and apply a second coat of varnish. Let this dry for 
hours. 

10. During the Periods necessary for drying processes, the work of 
nding the coils may be performed. See page 33. 

11. Place the supporting pieces M and M' in position, and insert 
e bolts b and b' in M. During this stage of the construction the struc- 
*re should be supported on a box or by blocks as indicated by B and B', 
^ure 10, high enough to allow the 12 inch bolts to be inserted from below, 
he bolts may be inserted from the top, in the piece M', to simply hold it 
mporarily in position. 

12. Proceed to lay the iron core strips in position as shown in figure 
,<). Consult figure 6, page 22, and figure 7, page 22. The two long strips 
, a', should be parallel with each other and at right angles with the shorter 
[id strip, e. Directly on top of the strips already laid in place, apply 
pother layer of strips as indicated in figure 11, page 28. 

Continue piling the strips, alternating the joints, until all of the longer 
•trips and one half of the shorter strips have been used. 

13. Place the strip S in position and bolt down firmly by means of 
the bolts b and b'. Just before the final turns are given to the nuts on 
b and b', the strips may be carefully lined up, by means of a small block 
and hammer, or by using a wooden mallet. The arrangement now ap¬ 
pears as in figure 9, page 27. 

14. If now the structure is tipped up on its end, n, n', figure 9, the 
piece M' may be removed, to allow the primary and the secondary coils 
to be slipped on over the limbs x and y of the iron core. 

It is very essential that both primary and secondary coils be well 
insulated from the connecting end yokes of the iron core. This may be 
accomplished by building up an insulating sheet using the scrap pieces of 
Empire Cloth, sticking them together with shellac varnish, and com¬ 
pressing the sheet between two flat boards under a heavy weight, while 
the shellac varnish hardens. The built up sheet may be about \ inch thick 


30 Designing, Making, and Operating High-Pressure Transformers 


shown at a, figure 12, page 31, and in figure 14, page 33; also in position 
on the transformer at a, figure 12. A sheet in the process of construction 
is shown at b, figure 14, and a finished one at a, same figure. Two such 
sheets are needed for each transformer, as shown in figure 16, page 35. 

To build up such a sheet, place a square piece of Empire Cloth, the 
desired size, on a flat board, and apply a coat of shellac varnish to its upper 
surface. Immediately place scrap pieces of the cloth on the varnished 
surface and apply a coat of varnish to their upper surface. Continue this 
process until the desired thickness is attained. Place another whole sheet 
of Empire Cloth over the top of the built up sheet, place a flat board on the 
completed built up sheet, and apply a weight of about 50 or 75 pounds. 
Allow the sheet to dry for twenty-four hours and then trim to the desired 
shape, with a sharp knife. By this process there is no waste of Empire 
Cloth, and a sheet of material having insulating qualities approaching 
those of mica is obtained at a small cost. 

15. Slip each tube, containing each section of the “primary” wind¬ 
ings, over each leg of the core, bending the terminals to allow the tubes 
separating the primary from the secondary windings to be slipped over 
the primary coils, after adjusting one of the insulating discs to the lower 
end of each separating tube, about 2 inches from the end. 

An excellent insulating separating tube may be constructed or “built 
up” by first gluing two layers of cardboard to form a tube of sufficient 
size to slip over the primary windings easily; applying a coat of shellac 
varnish to the outer surface, and immediately winding thereon in a spiral 
fashion, strips of Empire Cloth, about 1 inch wide, and about 5 feet in 
length. The winding should lap each other about \ inch, and after one 
complete winding has been finished, its surface may be coated with shellac 
varnish and another spiral wound on. The process may be continued 
until a tube of the proper thickness has been built up. After such a tube 
has been allowed to thoroughly dry, a strong tube having excellent insulating 
qualities is the result. 

The outside diameter of this separating tube should be slightly less 
than the inside diameter of the secondary pies. 

These separating tubes are shown at t, t', figure 12, page 31. 

16. Next slip on over the separating tube a pair of “pies” of the 
secondary winding, being arranged as explained under winding of secondary 
coils, page 33, until they rest against the end insulating disc. 

17. Proceed to add the secondary “pies”, to both limbs of the trans¬ 
former putting 16 single pies or 8 “units” on each limb. The units should 
be placed so that their terminals are all on the same line, to facilitate in 
joining them together. 


Designing, Making, and Operating High-Pressure Transformers 31 



Fig. 12. 

18. The units or pairs of pies should be placed relatively with each 
other so that when their terminals are connected with each other there 
will be a continuous winding, in the same direction, from one end of each 
limb to the other end of the same limb. That is, so that each half of the 
secondary winding shall consist of turns of wire all in the same direction 
of winding, and the two half sections of the complete secondary must be 
so connected with each other as to work properly together and not in 
“opposition”. 

Figure 3, page 12, will give an idea of the relation of the turns in the 
windings. 

19. The free ends of the “units” should be carefully cleaned, twisted 
together, and soldered by use of a small soldering iron. Do not use a lamp 
in soldering small wires. The heat of the flame tends to “burn” the wire, 
making a very poor joint and doing permanent injury to the wire. 

20. Properly connect the half-sections of the secondary with each 
other and bring the two end terminals to the top of hard rubber posts 
each \ inchin diameter, 3inches high, located as shown in figure 16, page 35. 
These hard rubber posts may be inserted in \ inch holes about 1 inch deep. 

21. The primary terminals may have flexible leads, soldered to them 
and brought out to four binding-posts, to allow various arrangements of 
connections. See figure 12. 

WINDING THE PRIMARY COILS. 

The primary windings require 18 pounds of No. 12 Double cotton 
covered (D. C. C.) B. & S. gauge, copper wire, wound double, two wires 
being wound side by side to form two layers, one having 40 turns, the other 



32 Designing , Making, and Operating High-Pressure Transformers 

having 60 turns, per section or per limb of the transformer. The total 
operative primary turns are therefore (40 + 60) x 2 = 200 TURNS. 
In reality there are 400 turns of wire; two sets of 200 turns each. The 
two sets connected" together in parallel constitute the 200 operative turns. 
This shows how an equivalent number of smaller wires may act as one large 
wire, and also renders witiding much easier; the two smaller wires being 
much more flexible than the equivalent single wire. 

The primary in one transformer was wound directly on the iron core, as 
rshown in figure 12, being insulated from the iron core by several layers of 
“Empire Cloth”; having a thickness of about 2V an inch. It might have 
.been wound on a form such as shown in figure 13, taken from the form, and 



Fig. 13. 


clipped on over the limb of the core. If wound in circular form, it allows 
the air to circulate through the spaces between the coil and the core, tend¬ 
ing to keep the temperature of the transformer, when in operation, at a 
low value. This however requires a greater length of wire. The arrange¬ 
ment of the winding form should be noted. The cylinder is mounted to be 
turned by the handle h, is provided with a speed-counter at i, for register¬ 
ing the number of turns, and has a diagonal cut cc' through it, so that its 
thinner ends may be screwed (screw at S) to the thicker ends thus holding 
the sections together. After a coil is wound, the screws at the ends may 
be removed, allowing the form to be easily withdrawn from the coil. The 
end bearing e and the handle h are removed by removing screws. 








Designing, Making, and Operating High-Pressure Transformers 33 

DIRECTIONS FOR WINDING THE SECONDARY COILS. 

The secondary of the transformer requires 20 pounds of No. 26^B. &. 
S. gauge, double cotton covered copper magnet wire. 



Fig. 14. 


This secondary is wound in “pies” or thin sections shown at e and f 
in figure 14, inches, internal diameter, 6f inches over all diameter, and 
f inch thick. Each pie is first wound on a form as shown in figure 15, 



carefully bound together with pieces of 
the No. 26 wire, to enable it to be re¬ 
moved from the winding form, and then 
soaked in melted paraffin, in a proper 
sized dish. When removed from the 
melted paraffin, and allowed to cool, 
the pie may be easily manipulated. 
Each pie should contain 800 turns of 
the No. 26 wire, and 32 pies are needed 
for the finished transformer, if 20,000 
volts are to be obtained. A set of fin¬ 
ished pies is shown in process of being 
assembled on the separating tube, at e 
and e', figure 12, page 31. 


Fig. 15. 




34 Designing , Making , and Operating High-Pressure Transformers 

The winding will be greatly facilitated if done in a lathe. 

A proper tension should be maintained on the wire while winding it 
and the wire should be continually guided from one side of the form to the 
other while winding, to prevent humps in the winding, or the slipping down 
of a turn between the turns already wound, and the side of the form. 

It should be noted that the tension on the wire while it is being wound# 
determines whether the number of turns stated may be wound in the given 
space. It is not considered advisable to wind the pies too tightly as this 
does not allow the hot paraffin to soak into their interior. 

A tube, t, figure 12, page 31, made of about 10 layers of Empire Cloth 
separates the primary from the secondary windings; while each secondary 
pie is separated from its neighbor by five discs put side by side to form an 
insulating separator about T V inch thick, shown at c, figure 14, page 33 
and in figure 12, page 31, cut from a sheet of the Empire Cloth. These 
discs are cut to fit closely to the tube separating the primary and second¬ 
ary, and having an outside diameter about one inch larger than the over 
all diameter of the secondary pies. The over all diameter of the separating 
discs may be 8 inches. A card board pattern used in cutting out the 
separating discs is shown at d, figure 14. If the transformer is to be 
immersed in oil, ordinary card board may be used in place of the Empire 
Cloth. 


APPROXIMATE COST OF MATERIALS. 

The following is an itemized account showing the approximate cost 
of the transformer just described. 


Wood for base. $ 1.00 

Casters. 1.34 

4 bolts, 12" x .20 

Iron strips for core, 82 § lbs. 9.00 

Wire for primary, 18 lbs., No. 12. 3.00 

Wire for secondary, 20 lbs., No. 26. 10.00 

Linseed oil, turpentine, and shellac. 1.00 

Paraffin wax. 1.20 

Binding posts. .40 

10 yards of Empire Cloth. 4.00 


















Designing , Making, and Operating High-Pressure Transformers 35 

The completed transformer is shown in figure 16, the secondary spark 
gap being made of copper wire bent into the shape of horns, arranged on 
sliding brass rods, supported by hard rubber posts. Flexible “drop cord” 
wires are used for primary connections. 

The purchase price of a transformer such as the one described, would 
probably be not less than $100.00. 



Fig. 16. 

OIL IMMERSED TRANSFORMERS. 

All high-pressure transformers will operate much more satisfactorily 
if surrounded with oil, such as paraffin oil, which belongs to the kerosene 
family. The oil is a liquid insulator that is self mending after a spark 
discharges through it, and acts to convey the heat away from the hottest 
portions of the transformer; preventing excessive heating. 

Good insulating oil called “transil” or transformer oil may be pur¬ 
chased for about 50 cents per gallon. 

To make an oil containing tank for a transformer, construct a box 
using soft pine boards about f- inch thick, large enough to allow the com¬ 
pleted transformer to be inserted with an all around clearance of about 1 
inch. Cover the outside of the box with thin sheet copper or ordinary 
“roofing” tin, carefully soldering all joints to prevent leaking of oil. A 
faucet may be soldered to one side near the bottom of the box to allow the 








36 Designing , Making , and Operating High-Pressure Transformers 

oil to be drawn off when desirable. The oil may however be syphoned 
from the box when necessary, by means of a flexible rubber tube or hose, 
doing away with a faucet, and preventing loss of oil by accidental opening 
of a faucet. 

If oil is employed as an insulator, cheaper separating insulation may 
be used, and much labor saved in constructing a transformer, as there will 
then be no need of soaking coils in melted paraffin. 

A word of caution may be valuable regarding the first trial of the 
completed oil immersed transformer. Never attempt to operate a high- 
pressure oil immersed transformer, for at least 24 hours after being placed 
in the oil. It requires time for the oil to completely soak into the interior 
of coils which contain many turns of wire. 

PRECAUTIONS. 

All material used in the construction of high pressure transformers 
should be carefully inspected for defects. The greatest care should be 
exercised in the various processes of construction to obtain the best pos¬ 
sible insulation of the various portions, the iron plates of the core, and the 
windings. The insulation of the different portions from one another may 
be tested by use of a telephone receiver and a single dry cell. 

The several coils should be individually tested to determine any broken 
wire that may exist. 

All coils should be carefully inspected and tested individually before 
assembling. 

Never use enameled wire in high-pressure transformer construction. 

Particular care in insulating is necessary, since it is the maximum value 
of an alternating-pressure that tends to puncture and break down insula¬ 
tion. 

For example, if the pressure wave is a sine-wave having a working 
value (effective) of 20,000 volts, the maximum value of this pressure is 
20,000 x 1.414; which is 28,280 VOLTS. 

The maximum value of a sine-curve is equal to the J/2 (square root 
of 2 = 1.414) times its effective value. 

CAUTIONS. 

The experimenter using high-pressure apparatus that is connected 
with service mains, should keep in mind that the source of energy is capable 
of supplying a considerable amount; meaning that personal contact with 
the high pressure side of the apparatus does not cause the input to the 
apparatus (and to the individual) to cease. The discharge of a Leyden jar 
or of a condenser through the body does not prove fatal, because the supply 


Designing , Making, and Operating High-Pressure Transformers 37 



of energy is not only limited, but is very quickly exhausted; so quickly in 
fact that the effect is not perhaps even harmful. The pressure in such a 
case may be much greater than that produced by an apparatus, which 
furnishing a much lower pressure continuously, is dangerous. Contact 
with the high-pressure terminals of a transformer should be guarded against* 
The ordinary frequencies offer no protection to the individual. A CON¬ 
TINUOUS CURRENT OF m (.03) OF AN AMPERE, IN A VITAL 
ORGAN, IS FATAL. 

Even though the resistance of contact through the two hands may be 
50,000 ohms, it is evident that 20,000 volts will send a current of § 

= § of an ampere through the body:— enough to kill a person several times. 

Always disconnect the double pole knife switch, connected with the 
primary, before touching any part of the secondary, with even one hand or 
with a stick. 

The secondary should be provided with fuses of small current capacity 
in addition to the primary fuses. 

In case of accidental short-circuit of the secondary, or in case of ac¬ 
cidental contact with the secondary, the small secondary fuses will blow 
out very quickly, offering better protection than offered by the larger 
primary fuses. 

Never attempt to adjust a high pressure wire with a screw driver, 
with the apparatus operating. 






38 Designing , Making, and Operating High-Pressure Transformers 

DATA APPLYING TO A 4,000 VOLT TRANSFORMER. 

AIK. W. transformer to transform from 110 volts at 60 cycles, to 
about 4,000 volts, is shown, in the process of construction in figures 17, 
and 18, pages 37 and 38. The ratio of transformation is 36.3. 



Fig. 18. 


The core consists of angle strips of Russia iron, 2| inches wide, bolted 
together as shown at b, figure 17, page 37 and in figure 18, to make a 
thickness of core of inches. The angle strips 
are cut from the sheet of iron as indicated in 
figure 19, to minimize waste of material. The 
longer leg of the larger angle piece is 10§ inches, 
and the shorter leg is 7f inches long or 13| inches 
and 10§ inches over all. This method of con¬ 
struction allows only two magnetic joints, and 
facilitates the taking apart of the device and 
the removal of the coils. One section of the core 
is shown at C, figure 17, page 37. The complete 
iron core weighs about 55 pounds. The primary 
consists of two coils, of No. 9 B. & S. gauge 
D. C. C. copper magnet wire, P and P', figure 17, 
page 37, each wound in two layers, 61 turns, per 



Fig. 19. 














Designing , Making , and Operating High-Pressure Transformers 39 


layer, making a total of 244 primary turns, all weighing about 9 pounds. 
The primary was wound on the winding form shown in figure 13, page 32, 
the form being 4 inches in diameter. Two layers of ordinary card board 
were first wound on the form and glued together, the wire being then wound 
on over the cardboard, tied together with tape, and the winding form re¬ 
moved. The inner diameter of the primary coils was 4| inches, and the 
over all diameter, 4f inches. The coils were given three coats of shellac 
varnish. 

The secondary consists of eight coils of No. 26 B. & S. gauge, D. C. C. 
copper magnet wire, wound on wooden* spools as shown at S in figure 17, 
page 37, and at S, S', figure 18; each spool containing about 1,100 turns of 
wire. As can be noticed in figure 17 and in figure 18 the wire was very 



Fig. 20. 

carefully wound, in even layers, which renders it possible to wind more 
turns in any given space. This transformer was designed for use without 
oil immersion, and without soaking the secondary coils in melted paraffin; 
being simply varnished over with shellac varnish. 

♦Dry soft pine is the best wood to use; dry white-wood being the’next in desirability. 









40 Designing, Making, and Operating High-Pressure Transformers 


The spools for the secondary were turned out in a wood-turning lathe, 
and had the following dimensions:— 

Over all, 6£ inches. Width over all, inches. 

Inner hole, 4|| inches. Width of winding space, if inches. 

Depth of winding space, Iff inches. 

The wooden spools were thoroughly soaked in hot paraffin and cooled 
before the secondary was wound onto them. The application of two coats 
of shellac varnish would answer in place of paraffin. 

Figure 18 shows one spool S", wound with wire, and seven empty 
spools. Figure 20 shows an arrangement for winding the wire.on to a 
spool f by means of the handle h. 

The spools are so wound that two may be placed adjacent to each 
other, the inner ends of the windings on the two spools coming together, 
so that when joined the two spools constitute one unit, of continuous wind¬ 
ing in the same direction. This allows the inner ends and the outer ends 
of wires from two units (or all the units) to be directly joined together, 
constituting a continuous winding, in the same direction, if any number 
of units are connected together. 

If taps are brought out from any single spool, a pressure of f the total, 
or about 500 volts may be obtained. One unit, two spools will give about 
1000 volts. 

Values of pressure of 500, 1000, 1500, 2000, 2500, 3000, 3500 and 4000 
volts may be obtained by making taps to proper points. 

POSSIBILITIES OF A TRANSFORMER AS A FREQUENCY 

CHANGER. 

All alternating-current waves are not true “SINE-CURVE” waves. 
When not sine-curve waves they are made up of the sum of a number of 
sine-curves, having different amplitudes and different frequencies from that 
of the so-called fundamental or resultant curve. 

Figure 21 shows an alternating-wave:—either an alterating-pressure 
or an alternating-current—that is made up of the sum of three sine-waves. 
Each point, (designated by being surrounded with a small circle) on the 
fundamental or resultant curve was located by adding, algebraically the 
* corresponding vertical heights of the three component sine-curves. 

Irregular shaped alternating-curves found in practice are made up of 
sine-waves having frequencies that are an odd number of times the fre¬ 
quency of their fundamental. An alternating-current wave having a 
frequency of 60 cycles per second, may be made up of four separate sine- 
waves, having frequencies of 1, 3, 5, and 7 times 60: namely, 60, 180, 300 


Designing , Making , and Operating High-Pressure Transformers 41 



Fig. 21. 




























































































42 Designing , Making , and Operating High-Pressure Transformers 


and 420 cycles respectively per second. By low values of magnetic 
flux in the iron core of a transformer, by a small primary current, one of the 
component frequencies of the fundamental maj^ be brought into promi¬ 
nence, and thus the transformer, in a degree, can be made to act as a fre¬ 
quency changer; the changes of course being limited in number. Many 
current-curves in practice have been found to consist of as many as 27 
component sine-curves, the frequency of each being an “odd” number of 
times that of the fundamental. 

Transformers arranged on three-phase circuits may be well adapted 
for frequency changers, acting on the principle of magnetic supersaturation. 
The “ efficiency ” of frequency changers based upon the foregoing principle 
will not be high. 

HOW TO OBTAIN UNITY POWER FACTOR. 

It is undesirable that any alternating-current device should operate 
at a low power factor, since this condition means increased losses, a greater 
first cost, and an attendant increased operating expense. 

Any method of keeping the power factor at a high value, (the greatest 
value being unity) is valuable so far as increase in operating efficiency is 
concerned. 

A “ condenser” connected with any coil which has inductance, will tend 
to increase the power factor, and if the proper numerical relation exists 
between the “capacity” of the condenser and the coefficient of inductance 
of the coil, a power factor of unity may be expressed by: 

2 t rf C = - ■ \ ; (13) from which may be obtained: 

2tJL 

C = ■ ■ 2 -/* 2 t ■ Here C denotes the capacity of a condenser, ex- 
471- J L 

pressed in farads: f denotes the frequency of the applied pressure; L de¬ 
notes the coefficient of inductance, expressed in henrys, and tt as usual, 
denotes the number 3.1416. See page 3. 

It should be observed that the larger the value of L the less the re¬ 
quired value of C, to produce unity power factor at any fixed frequency. 
This means that for a large coil of many turns with a large iron core, a 
condenser having a small capacity is needed to produce a power factor of 
unity. A condenser connected in series or in parallel with the primary of 
a transformer, improves the power factor. 

Likewise a condenser connected with the secondary improves the power 
factor of the secondary, and greatly increases the sparking ability of high- 
pressure transformers. 




Designing , Making , and Operating High-Pressure Transformers 43 


A condenser used in connection with the high-pressure secondary has 
a much smaller capacity, and is constructed differently from a condenser 
which is to be connected with the low pressure primary. Any condenser 
that is to be used with high pressures must be made of thick metal plates, 
very carefully insulated with thick glass plates, and immersed in oil; while 
a condenser for low pressures may be made of ordinary tin foil, separated 
by thin paraffined paper. 

The following numerical example will be given: TO FIND THE 
CAPACITY OF A CONDENSER THAT WILL NEUTRALIZE THE 
INDUCTANCE OF THE PRIMARY COIL OF A TRANSFORMER 
WHOSE COEFFICIENT OF INDUCTANCE L = § HENRY, IF THE 
FREQUENCY OF THE APPLIED PRESSURE IS 60 CYCLES PER 
SECOND. 


Making the proper numerical substitutions in equation (13), page 42 
gives: 

C = • QQQQ ^ 7Q3 - = 2 X .0000070362 

DATA. 


= . 0000140724farad. 


which is equal to 


0000140724 

1000000 


= 14.072 microfarads. 


ir = 3.14159 
7T 2 = 9.8696 
/ =60 cycles, 

f 2 = 3600 
L = \ henry. 


(One farad is equal to 1000000 microfarads) 

- ~»~2 = .0000070362 

(2 7 rj) 


Next suppose the inductance of the secondary of the above transformer 
is 50 henrys; find the numerical value of the capacity of a condenser to give 
a unity power factor. 

In this case: 


C = •Q 00007036 - 2 = .00000014072 farad: or 

50 

,00000014072 = 0.1407 MICROFARAD. 
1000000 


The greater inductance of the high-pressure circuit of a transformer 
is because of the greater number of turns of wire constituting this circuit. 







44 Designing , Making, and Operating High-Pressure Transformers 

Inductance varies directly as the square of the number of turns on any given 
coil. Doubling the number of turns increases the inductance fourfold. 

Another term for unity power factor is “resonance”. 

One of a number of odd harmonics may be rendered prominent by 
connecting a condenser (in series) with the secondary of a transformer and 
producing “ resonance” with an odd harmonic instead of with the funda¬ 
mental itself. 

Applying the foregoing principle, the value of a capacity that will 
produce resonance with the third harmonic frequency may be found. If 
the applied pressure has a frequency of 60 its third harmonic is 3 x 60 = 
180 cycles per second. In this case: 

c 3 = 1 _ = 1 _ 

3 4tt 2 X 180 2 X i 39.478 X 32400 x \ 

= --- = . 00000156 farad. 

1279100 

= 1.56 MICROFARAD. 

A condenser having this capacity, connected with the primary, would 
tend to bring the third harmonic frequency into prominence, causing the 
arrangement to act as a frequency changer, from 60 to 180. 

The value of a capacity to reinforce th e fifth harmonic would be: 

C 5 = -L - = _- = 0 562 MICROFARAD. 

39.478 x 300 2 x | 

A condenser having this capacity will tend to make prominent a fre¬ 
quency of 300 cycles per second. By using a variable condenser properly 
graduated, the different odd harmonics may be rendered prominent. For 
this particular primary a condenser having a capacity of 0.3 microfarad 
will bring out the seventh harmonic. 

METHODS OF CONNECTING PRIMARY COILS TO PRODUCE 
DIFFERENT SECONDARY PRESSURES. 

The induced secondarj^ pressure in any transformer depends upon the 
magnitude of the applied primary pressure. 

If pressure is used that is supplied from so-called constant pressure 
mains, it is impossible, with a coil having a single winding, to increase the 
induced secondary pressure; it may however be readily reduced by connect¬ 
ing resistance, (either inductive or non-inductive) in series with the single 
coil. 






Designing , Making , and Operating High-Pressure Transformers 45 

With two primary coils, on the other hand, a method for varying the 
secondary pressure may be employed, by first connecting the two primary 
coils in series. The two coils may next be connected together in parallel, 
with resistance in series with the parallel arrangement of the two coils. 
By varying the amount of the resistance, the applied pressure may be 
varied as desired. 

If the applied primary pressure is 110 volts, and the two primary coils 
are connected in series, the pressure applied to each coil is 55 volts. When 
the two coils are connected with 110 volt mains, each coil receives an ap¬ 
plied pressure of 110 volts instead of only 55 as when the coils were in 
series. Much more current in the coils is the result, according to equation' 
(1), page 7, and the flux density in the iron core is greatly increased ac¬ 
cording to equation (11), page 18. 

Another way of expressing the matter would be based upon the con¬ 
dition that the pressure per turn of both primary and secondary is the same. 
If the pressure per turn of the primary is increased, then the pressure per 
turn of the secondary is also increased. 

EXAMPLE. Suppose the primary of a transformer consists of two 
coils, each having 110 turns of wire, while the secondary of the same trans¬ 
former consists of two sections or coils, each having 2200 turns. 

If the two primary coils are connected in series and 110 volts applied, 
the primary per turn pressure will be = \ volt. If the per turn pres¬ 
sure of the secondary is also \ volt, the secondary terminal pressure will be 
2200 volts, provided the secondary coils are also connected in series. If 
the secondary coils in this case should be connected in parallel, the secon¬ 
dary terminal pressure would of course be 1100 volts. 

Now assume that 110 volts is applied to each individual primary coil," 
the two coils being in parallel. The per turn pressure will be one volt. The 
induced secondary pressure will be 1 volt per turn; giving a secondary 
terminal pressure of 4400 volts if the two secondary coils are in series, and 
2200 if they are in parallel. 

With the latter arrangement, care w T ill need be taken that the coils are 
not overheated. 

If two similar transformers have their primarys connected with the 
same supply mains, and their secondaries connected in series with each 
other the combined terminal pressures will be double that of a single trans¬ 
former. If ten transformers, each giving a secondary terminal pressure of 
100,000 volts, have their primaries all connected together in parallel and to 
the same service mains, while their secondaries are all properly connected 
together in series, the combined terminal pressure would l^e 1,000,000 volts, 
which would produce a vigorous spark. 


46 Designing, Making, and Operating High-Pressure Transformers 

PRICE OF MATERIALS FOR BUILDING THE HIGH PRESSURE 
TRANSFORMER DESCRIBED ON PAGE 26 OF THIS BOOK, 
AND FOR BUILDING THE TRANSFORMER AS PER 
PAGE 38. 

Iron strip for Core.20 cts per pound. 

Wire for Primary.25 cts per pound. 

Wire for Secondary.35 cts per pound. 

Bolts and Screws.30 cents. 

Paraffin Wax.15 cts per pound. 

Binding Posts.15 cts. each. 

Empire Cloth.40 cts. per yard. 

Prices subject to change without notice. Remit amount with order to 


ENGINEERING EDUCATION EXTENSION 


BOX 41. 


HANOVER, N. H 










Important References Relating to 
Transformers 

Abnormal Voltages in Transformers; by J. M. Weed, A.I.E.E., 
Aug., 1915. 

The Design of Stationary Transformers; Electrical World, Aug. 28, 
1915, page 459. 

The Determination of the Ratio of Transformers and of the 
Phase Relations in Transformers; Bulletin, National Bureau of 
Standards, Oct., 1909. 

Effect of Third Harmonic in Voltage Wave; by R. C. Powell, Elect. 
World, Jan. 16, 1915. 

Harmonics in Transformer Magnetizing Currents; by J. F. Peters, 
A.I.E.E., Aug., 1915. 

Influence of Transformer Connections on Operation; by Louis F. 
Blurr.e, A.I.E.E., May, 1914. 

Grounding of Secondaries; Electrical World, May 4, 1911. 

Grounding of the Secondary; Electrical World, June 30, 1910. 

Methods of Grounding Transformer Secondaries and Secondary 
1 Networks; Electrical World, June 1, 1912. 

Standard Methods of Grounding Secondaries of Transformers; 
Journal of Electricity, Power and Gas, San Francisco, California, 
Sept. 20, 1913. 

Observation of Harmonics in Current and in Voltage Wave Shapes 
of Transformers; by John J. Frank, A.I.E.E., May, 1910. 

Notes on Multiple Operation of Transformers; by W. J. Wool¬ 
dridge, Gen. Elect. Review, Oct., 1908. 

Parallel Operation of Transformers; by E. G. Reed, Electrical 
World, July 18, 1908. 

Parallel Operation of Stationary Transformers; by J. M. Weed, 
Electrical World, Nov. 21. 1908. 

Parallel Operation of Transformers; by H. Bewlay, Electrical 
World, Nov. 21, 1908. 

Parallel Operation of Transformers; by W. V. Lyon, Electrical 
World, Feb. 7, and 14, 1914. 

Parallel Operation of Transformers; by J. B. Gibbs, Electric Jour¬ 
nal, May, 1909. 

Problems on the Operation of Transformers; by F. C. Green, 
A.I.E.E., Feb., 1911. 

Ratings of Single Phase Transformers for Grouping on Polyphase 
Circuits; by H. C. Soule, Electric Journal, April, 1910. 

Polarity of Single-Phase Transformers; by M. A. Smith, Jr., Elec¬ 
trical Journal, Feb., 1915. 

What Is the Ratio of a Transformer? by M. G. Lloyd, Electrical 
World, July 11, 1908. 

Wiring and Connections for Constant Potential Transformers; Geo. 
A. Burnham, Elect. World, Oct. 5, 1907. 


Books for Teachers, Students 
and Amateurs 

By PROF. F. E. AUSTIN, Box 441, Hanover, N. H. 

“Directions for Designing, Making and Operating High Pres¬ 
sure Transformers,” postpaid, 65 cents. 

This book is written for those Experimenters who desire to con¬ 
struct their own apparatus, and contains a large number of working 
directions and useful hints. It describes the making of a “Step-up” 
transformer giving 20,000 volts for Wireless Telegraphs and Tele¬ 
phones, and for operating tube lamps, X-ray tubes, etc. The book is 
well illustrated, showing special methods of procedure, fundamental 
theories and finished apparatus. It is plainly written and the math¬ 
ematical matter is treated in quite a simple way. It is full of new 
ideas relating to methods of design and construction. 

REVIEW FROM THE WIRELESS WORLD. 

June, 1916, London, Eng. 

“Directions for Designing, Making and Operating High Pressure 
Transformers,” by Professor F. E. Austin, Hanover, N. H.: 
Professor F. E. Austin. 3s. net. 

This is an interesting and clearly written little book, particularly 
valuable to the serious student of wireless and to the operator who is 
anxious to understand thoroughly the principles and construction of 
the component parts of his installation. 

The author introduces the subject by referring to the commercial 
demand andj necessity for electric power at high pressure, and the 
reasons why alternating current is the most useful for this purpose. 
A simple but very practical explanation of the construction of the 
transformer then follows, after which we find an explanation of sym¬ 
bols and annotation, the various losses in a transformer, power factor, 
and other matters. The author next treats of the design of a 20,000 
volt transformer, entering very carefully into practical details of cal¬ 
culation. Following this, we have a chapter entitled “Directions and 
Data for Constructing a 3-KW. 20,000 volt Transformer,” the approx¬ 
imate cost of materials not being overlooked. A further chapter deals 
with data applying to a 4,000-volt transformer. 

We do not remember having previously seen any small book deal¬ 
ing so thoroughly and practically with the construction of high pres¬ 
sure transformers, nor one in which the diagrams and photographic 
illustrations were so happily chosen. The impression we have gained 
after reading the book is that the author knows exactly what he is 
talking about and how to express himself. 



















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